Calibration in RIS-Aided Localization Systems

Reconfigurable intelligent surfaces (RISs) offer significant potential for enhancing both communication and localization performance in wireless networks. While communication relies on end-to-end channels without the need of knowing anchor states, localization requires precise knowledge of RIS states for channel parameter extraction. Such states include the position, orientation, and possibly hardware impairment (e.g., RIS element failures) of the RIS. However, obtaining accurate state information can be challenging in practice. This book chapter focuses on the practical calibration challenges of RIS-aided localization systems. The chapter begins with a system model description, emphasizing the distinction between localization and calibration problem formulations. It proceeds to explore various performance metrics, configurations for RIS profiles, and estimation and detection methods for calibration tasks. Specifically, three case studies are discussed: (i) joint RIS calibration and user equipment positioning, (ii) bistatic sensing of RIS targets, and (iii) joint RIS element failure detection and localization, with calibration algorithms provided. Finally, simulation results for the mentioned calibration scenarios are presented, followed by the conclusion and outlook on future developments of RIS-aided networks.